Vanilla ice cream with chocolate magic shell
Making ice cream at home seems relatively simple — make a custard base, churn then freeze — but the chemistry and thermodynamics involved in producing the perfect scoop means that it is kind of tricky to produce an ice cream that isn't too icy and actually freezes properly.
If you understand the reactions that occur during the process of making ice cream, from the crème anglaise stage to final storage in the freezer, you can make your next batch smoother and creamier than ever before. Follow these steps for ice cream that will make you forget about making a run to one of those chains that boast 29, 30 or maybe 31 different flavors.
Custard is king
First, we need to discuss the foundation for any proper ice cream: the custard base. Ice cream is classified as a sweet stirred custard, which involves thickening a mixture of egg yolks, sugar and dairy through a combination of slow heat and agitation. The goal is to slowly heat the egg yolks to a temperature at which the proteins coagulate; however, if done too quickly, the proteins will coil too tightly, both diminishing the thickening capabilities and turning the mixture watery. Fat helps to dilute the protein matrix, making the proteins less likely to collide with one another and curdle, so using a higher ratio of heavy cream to milk will lead to a richer, thicker custard.
Sugar choice is important
Next, the quantity and types of sugar used will impact the freezing of the final product. Using an invert sugar — a mixture of glucose and fructose — causes the custard base to freeze more rapidly, form smaller ice crystals and remain harder at room temperature. For the home cook, this means using something as easily accessible as light corn syrup to supplement some or all of the sugar in the recipe. As water molecules attempt to flow through the custard base and join, forming large ice crystals, the starch chains within the corn syrup prevent them from attaching, thus leading to smaller ice crystals. Having a higher freezing point is also important because many home freezers are prone to constant thawing and refreezing. Ever opened your half-eaten pint of Häagen-Dazs to find a thin veneer of ice crystals sitting on top? Your persnickety freezer is to blame. Inverted sugar should help prevent that from happening.
Use vanilla properly
A flavor note: Most ice cream recipes call for vanilla in some form. If you’re making vanilla ice cream, it’s worth the extra splurge on fresh vanilla beans or vanilla paste. However, many of us opt to use vanilla extract. If you go the extract route, make sure the custard base has cooled before adding the vanilla. Vanilla extract is made by steeping vanilla beans in a neutral alcohol, like vodka, for an extended period of time until the flavor has absorbed into the liquid. As soon as you introduce heat to the equation, the alcohol begins to gently cook off, leading to a diminished flavor.
When it comes time to apply heat, it is crucial to gently cook the egg proteins, lest they bond together tightly and leave behind solid bits of scrambled egg yolk in the custard. The method for doing this is called tempering, which involves constantly whisking the egg yolk-sugar mixture while slowly introducing the hot dairy mixture. Slowly elevating the temperature of the eggs keeps the custard smooth and void of any of that off-putting cooked egg flavor. Next, the custard mixture needs to be heated to 180 degrees while constantly stirring with a rubber spatula. Normally, egg yolks solidify at 150 degrees; however, the sugar and the liquid interfere with the protein bonds and raise the temperature to 180 degrees. If the yolks do not reach 180 degrees, their proteins will not have uncoiled enough to form the gel structure we need for good ice cream. An instant-read thermometer will help you gauge this most accurately.
For the smoothest ice cream possible, be sure to completely chill the custard before churning. Smooth is just a tactile sensation on our palates when the ice crystals are so small that they’re nearly undetectable. Freezing the ice cream base as quickly as possible is the most surefire way to achieve this. In fact, the one drawback to making ice cream from scratch at home is the fact that most home models of ice cream churns take at least 35 minutes to freeze their contents, while many larger commercial machines freeze in under a minute.
In order to best overcome this problem, take a few extra chilling steps: Once your custard has thickened, immediately chill it in an ice bath. If you’re using a cylindrical churning device, make sure the bowl has frozen for 48 hours, as the friction from the machine will start to thaw some of the ice. Reserve 1 cup of the custard base and place it in a container in the freezer, while placing the remaining mixture in the refrigerator. Once the custard in the freezer is solid, pass it through a wire mesh strainer into the refrigerated custard base to help make it even colder. Immediately pour it into the canister to start churning.
Any store-bought ice creams that boast being “slow-churned,” “double-churned” or “premium-churned” are simply selling empty marketing buzzwords. Look carefully at the labels and you’ll see that the “slow-churned” varieties are all low-fat and low-sugar, with a variety of additives, synthetic ingredients and modified starches to help account for the texture. Cream, egg yolks, inverted sugar and speed win out over Propylene Glycol Monostearate and polydextrose any day of the week.
Finally, transfer the semi-frozen ice cream to the freezer as quickly as possible. Because of the mercurial nature of most home freezers, it’s important to select the right vessel for freezing. Instead of immediately scooping the ice cream into a tall, cylindrical container, spread it out in a thin layer on a baking sheet. The larger surface area will help your ice cream solidify much faster than in a deeper vessel. Once frozen, transfer to an airtight container and keep in the coldest part of your freezer. Following each of these steps will help you produce smoother, creamier ice cream than ever before.